Reaction sensor

Pitts JR (2002) Detecting hydrogen with chemochromic thin films. Ind Physicist (AIP) Forum June/July 31 Polla DL, White RM, Muller RS (1985) Integrated chemical-reaction sensor. In Digest of technical papers of TRANSDUCERS 85. 1985 International conference on solid-state sensors and actuators, 11-14 June 1985, Philadelphia, pp 33-36... 

Figure 11.39 summarizes the reactions taking place in this amperometric sensor. FAD is the oxidized form of flavin adenine nucleotide (the active site of the enzyme glucose oxidase), and FAD1T2 is the active site s reduced form. Note that O2 serves as a mediator, carrying electrons to the electrode. Other mediators, such as Fe(CN)6 , can be used in place of O2. 

Safety has been greatly increased by use of the continuous nitration processes. The quantity of nitroglycerin in process at any one time is greatly reduced, and emulsification of nitroglycerin with water decreases the likelihood of detonation. Process sensors (qv) and automatic controls minimize the likelihood of mnaway reactions. Detonation traps may be used to decrease the likelihood of propagation of an accidental initiation eg, a tank of water into which the nitrated product flows and settles on the bottom. 

Chemical and biological sensors (qv) are important appHcations of LB films. In field-effect devices, the tunneling current is a function of the dielectric constant of the organic film (85—90). For example, NO2, an electron acceptor, has been detected by a phthalocyanine (or a porphyrin) LB film. The mechanism of the reaction is a partial oxidation that introduces charge carriers into the film, thus changing its band gap and as a result, its dc-conductivity. Field-effect devices are very sensitive, but not selective. 

Immobilized Enzymes. The immobilized enzyme electrode is the most common immobilized biopolymer sensor, consisting of a thin layer of enzyme immobilized on the surface of an electrochemical sensor as shown in Figure 6. The enzyme catalyzes a reaction that converts the target substrate into a product that is detected electrochemicaHy. The advantages of immobilized enzyme electrodes include minimal pretreatment of the sample matrix, small sample volume, and the recovery of the enzyme for repeated use (49). Several reviews and books have been pubHshed on immobilized enzyme electrodes (50—52). 

Multienzyme Electrodes. Coupling the reactions of two or more immobilized enzymes increases the number of analytes that can be measured. An electro-inactive component can be converted by an enzyme to a substrate that is subsequentiy converted by a second enzyme to form a detectable end product (57). For example, a maltose [69-79-4] sensor uses the enzymes glucoamylase and glucose oxidase, which convert... 

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors (qv) require multiple steps for analyte determination, and either sandwich assays or competitive binding assays maybe used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. In the sandwich assay type, the membrane-bound antibody binds the sample antigen, which in turn binds another antibody that is enzyme-labeled. This immunosensor is then placed in a solution containing the substrate for the labeling enzyme and the rate of product formation is measured electrochemically. The rate of the reaction is proportional to the amount of bound enzyme and thus to the amount of the analyte antigen. The sandwich assay can be used only with antigens capable of binding two different antibodies simultaneously (53). 

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

Premature disk failure Operator error Pump motor failure Reaction inliibitor system failure Coolant system failure Outlet piping obstruction Motor alann failure Pressure sensor failure... 

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